GREGORY PETSKO: For thousands of years, long before there was such a thing as a science of chemistry, people were fascinated by plants, because they knew that plants contained substances that could affect people. Coffee will keep you awake. Tobacco contains something that will calm your nerves. Foxglove contains an extract that'll affect your heart. And the whole goal of chemistry in the early part of the 20th century was to understand what these natural products were, to characterize their chemical structures, and figure out how to make them. This was called "natural products chemistry." It was the main branch of chemistry. And in 1929, Vienna, in Austria, was the seat of natural products chemistry. And that's why Percy Julian went there.